The present invention relates to a photomask pattern correcting method for correcting a pattern of a photomask used when exposing in a lithography process which is one of the manufacturing processes of a semiconductor device, and to a photomask corrected by the same, and to a photomask pattern correcting device.
In a lithography process, which is one of the manufacturing processes of a semiconductor device, various types of light energies such as visible light, UV light, or electron beam are projected on a target for exposure so as to transfer a desired pattern thereon.
In recent years, more refined and highly integrated semiconductor elements have been developed. In response to this, in the lithography technique, in order to achieve a minimum processing dimension of not more than 0.1 xcexcm, a super resolution lithography technique capable of processing with a dimension substantially the same as or less than the wavelength of the exposing light has been developed for practical use.
The practical limit of a resolution of pattern exposure is determined by various factors. Of those factors, in response to refining of patterns in recent years, the optical proximity effect has been one of the main factors determining the resolution limit. The proximity effect refers to a problem which is caused by the interference effect of a radiation energy such as light between proximate patterns. Such a problem includes deformation of a transfer pattern caused by interference within a single pattern.
In the conventional lithography process, since the size of a transfer pattern is sufficiently large compared with the wavelength of exposing light, the problem of proximity effect is not caused. In the super resolution lithography technique, however, the proximity effect phenomenon is a big problem.
When the size of a transfer pattern is substantially the same as or less than the wavelength of exposing light, due to the proximity effect phenomenon and receding of edges (especially at line end) and a pattern deformation phenomenon of a photoresist during development, a difference in line-width and shape is generated between a pattern of a photomask and a pattern transferred onto the photoresist.
For this reason, in the super resolution photolithography, in order to form a photoresist having a desirable pattern, it is one of the most important techniques to accurately estimate the degree of deformation due to the optical proximity effect, etc., generated when transferring, and to correct a photomask pattern. The same can be said for the lithography technique adopting an electron beam which has a large interaction, or other types of light energies.
To present, various attempts have been made to correct a photomask pattern by accurately estimating the optical proximity effect. For example, Japanese Unexamined Patent publication No. 189913/1990 (Tokukaihei 2-189913) discloses a method of correcting a photomask pattern with respect to the optical proximity effect.
In the above publication, an improvement is made at a semiconductor element level; however, in practice, correction at a chip level, i.e., a large area of approximately several tens of millimeters square is required.
An example of correction with respect to the optical proximity effect at a chip level or at a block level is suggested in the following publication: S. Miyama, K. Yamamoto, et al., xe2x80x9cLarge area optical proximity correction with a combination of rule-based and simulation-based methodsxe2x80x9d, Jpn. J. Appl. Phys. Vol. 35 (1996/12) pp. 6370-6373.
The following describes the correction steps with respect to the proximity effect carried out in the above conventional example referring to the flowchart of FIG. 13, and FIG. 14 and FIG. 15.
First, a distribution of light intensity in a projected image is determined from a pattern 30 of the photomask shown in FIG. 14, and a critical edge (transparent pattern edge or opaque pattern edge of pattern 30) subject to correction with respect to the optical proximity effect is extracted (S41 and S42). In FIG. 14, the hatched portions indicate opaque portions, and the other portions indicate transparent portions (translucent portions) . Also, in FIG. 14, the critical edge is indicated by the heavy broken line E.
Then, an appropriate point for determining a correction amount of the critical edge E is set as a correction point, and a 1D (one dimensional) context of the correction point is determined (S43). Namely, a binary judgement is performed with respect to a correction point on the arrow C of FIG. 14 (for example, correction point P indicated by xc3x97 in FIG. 14) so as to determine the 1D context which is bit map data representing the transparent portion and the opaque portion indicated by xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d, respectively.
Thereafter, it is judged in S44 whether the 1D context thus determined coincides with any one of 1D contexts prepared beforehand in a correction table of FIG. 15. If it is judged in S44 that the 1D contexts coincide, the correction amount is determined referring to the correction table so as to correct portions of the photomask pattern requiring correction to the correction amount thus determined (S47). Note that, the broken line in FIG. 15 indicates the correction point P.
On the other hand, in the case where the determined 1D context does not coincide with any of the 1D contexts in the correction table, a correction amount appropriate for the determined 1D context is calculated by simulation (S45), and the determined 1D context and the correction amount determined in S45 are added to the correction table so as to update the correction table (S46). Then, the correction point is replaced with another correction point appropriate for determining the correction amount for the critical edge E (S43), and a correction amount is determined referring to the updated correction table so as to correct, in the same way as above, portions of the photomask pattern requiring correction to the correction amount thus determined (S47).
The sequence of S43 through S47 is repeated until correction is finished with respect to all the correction points of the edge extracted in S42 (S48), and when correction is finished with respect to all the correction points, the process is finished.
However, in the photomask pattern correcting method of the described conventional example, contrast and gradient of light intensity are determined from a distribution of light intensity in a projected image, and a critical edge is determined with respect to target pattern dimensions so as to carry out correction with respect to the optical proximity effect in the photoresist.
That is to say, in the photomask pattern correcting method of the conventional example, it is impossible to carry out, along with the correction with respect to the optical proximity effect, correction with respect to photoresist development and a difference in underlayer level by extracting a critical pattern range associated with receding of edges and pattern deformation of the photoresist generated during development, and line-width shifting, etc., of the photoresist due to the difference in underlayer level.
As a result, the photoresist pattern deviates from a desired pattern due to the receding of edges and pattern deformation of the photoresist, or the line-width shifting. In other words, the photomask pattern correcting method of the conventional example has a problem in that accurate correction cannot be carried out.
Further, in the photomask pattern correcting method of the conventional example, it is required that (1) simulation of a projected light optical image, (2) a calculation by simulation of photoresist exposure and development, and (3) a preparation of a correction table are carried out with respect to all regions requiring correction. As a result, a large amount of measurement data are required to be prepared in advance and an extremely long time is required for calculation, preventing fast correction from being carried out.
It is an object of the present invention to provide a photomask pattern correcting method and a photomask pattern correcting device respectively capable of carrying out accurate and fast correction with respect to a photomask pattern, and a photomask corrected by the-same.
In order to achieve the above-mentioned object, a photomask pattern correcting method in accordance with the present invention for forming a desired photoresist pattern on a wafer by developing a photoresist after exposure through a photomask includes the steps of (1) receiving, at a time, pattern data representing patterns of a plurality of photomasks, (2) automatically extracting, from an entire region of each of the plurality of photomasks on the pattern data, a development correction range which requires being corrected with respect to receding edges (especially at line end) and pattern deformation of a photoresist generated during development, (3) correcting, with respect to development of the photoresist, the photoresist within only the development correction range, (4) automatically extracting, from the entire region of each of the plurality of photomasks on the pattern data, an underlayer correction range which requires being corrected with respect to an optical proximity effect due to a base structure of the photoresist, and (5) correcting, with respect to the base structure of the photoresist, the photoresist within only the underlayer correction range.
In the described method, correction is carried out with respect to photoresist development, along with correction with respect to a base structure of a photoresist. Thus, it is possible to accurately correct a photomask pattern with respect to both of (i) receding edges (especially at line end) and a pattern deformation phenomenon of a photoresist dependent on a photoresist and pattern density, which occur during development and (ii) the optical proximity effect due to an optical difference in underlayer level, which become problems in a pattern with processed dimensions not more than several times the wavelength of exposing light.
Further, since correction is carried out after extracting a range requiring correction, correction of a photomask pattern can be carried out efficiently, thereby realizing fast correction of a photomask pattern.
Also, the described method includes an optical proximity effect correcting step which basically carries out correction with respect to the optical proximity effect in a photoresist, thereby realizing accurate photomask pattern correction for the optical proximity effect in a photoresist.
In order to achieve the afore-mentioned object, another photomask pattern correcting method is provided in accordance with the present invention for forming a desired photoresist pattern on a wafer by exposing a photoresist by an exposing device through a photomask which has been made by a photomask drawing device. A region whose distance from an edge of the photomask is not more than a predetermined value is designated as an optical proximity effect effective range based on (1) an exposure wavelength, a numerical aperture, and a coherent factor of the exposing device and (2) a minimum feature size of the photomask drawing device so as to carry out correction with respect only to the optical proximity effect effective range.
With this method, it is possible to effectively and accurately correct a pattern shift of a photomask pattern, which becomes a problem in patterning of a fine photomask, caused physically and chemically by a phenomenon such as an edge receding phenomenon during photoresist development which is dependent on an optical proximity effect and pattern density, thus making it easier to automate the photomask pattern correction technique including the correction of the optical proximity effect.
In the above methods, it is preferable to determine a transparent pattern density in the optical proximity effect effective range, and to carry out correction for a pattern size shift during photoresist development with respect only to a region whose transparent pattern density is not less than a threshold value if the photoresist is positive type.
In this manner, the transparent pattern density of a photomask used in a certain step of a semiconductor manufacturing process is determined in the optical proximity effect effective range, and it is judged, based on a comparison between the transparent pattern density and the threshold value whether to carry out correction with respect to the pattern size shift during photoresist development. Next, correction with respect to the pattern size shift during photoresist development is carried out with respect only to a region whose transparent pattern density exceeds the threshold value. As a result, it is possible to more efficiently carry out the photomask pattern correction, and reduce the processing time.
Incidentally, when the xcex3 value is large, development is carried out with an amount of light which exceeds a certain amount; thus, the shape of the photoresist after development is determined substantially with the threshold value of light intensity. On the other hand, when the xcex3 value is small, the shape of the photoresist after development becomes dependent on the exposure amount and the slope (distribution) of the exposure amount, and a pattern shift is generated. Thus, as the xcex3 value becomes smaller, occurrence of pattern shift during photoresist development is increased.
In order to overcome this problem, in the above methods, it is preferable to determine the region in which correction with respect to the pattern shift during photoresist development should be carried out based on the threshold value which is determined from the xcex3 value representing the exposure sensitivity of the photoresist. As a result, it is possible to efficiently and accurately correct the photomask pattern regardless of the exposure sensitivity of the photoresist.
Note that, in the above methods, the predetermined value is determined by (axcex/NA)+xcex4, xe2x80x9caxe2x80x9d being a positive coefficient which is determined in accordance with the coherent factor of an exposing device, xcex being the exposure wavelength of the exposing device, NA being the numerical aperture of the exposing device, and xcex4 being the minimum feature size of a photomask drawing device.
In order to achieve the afore-mentioned object, a photomask in accordance with the present invention is pattern-corrected by any one of the described pattern correcting methods.
With the described methods, it is possible to provide a photomask which allows a desirable photoresist pattern to be formed on a wafer even when a pattern shift dependent on the optical proximity effect and a pattern density, such as an edge receding phenomenon, is generated during photoresist development.
In order to achieve the afore-mentioned object, a photomask pattern correcting device for forming a desired photoresist pattern on a wafer by developing a photoresist after exposure through a photomask includes (a) a pattern data input section for receiving, at a time, pattern data representing patterns of a plurality of photomasks, (b) a development correction range extracting section for automatically extracting, from an entire region of each of the plurality of photomasks on the pattern data, a development correction range which requires being corrected with respect to receding edges (especially at line end) and pattern deformation of a photoresist generated during development, (c) a development correcting section for correcting, with respect to development of the photoresist, the photoresist within only the development correction range, (d) an underlayer correction range extracting section for automatically extracting, from the entire region of each of the plurality of photomasks on the pattern data, an underlayer correction range which requires being corrected with respect to an optical proximity effect due to a base structure of the photoresist, and (e) an underlayer correcting section for correcting, with respect to the base structure of the photoresist, the photoresist within only the underlayer correction range.
In the described arrangement, correction is carried out with respect to photoresist development, along with correction with respect to a base structure of a photoresist. Thus, it is possible to accurately correct a photomask pattern with respect to both of (i) receding edges and a pattern deformation phenomenon of a photoresist dependent on a photoresist and pattern density, which occur during development and (ii) the optical proximity effect due to an optical difference in underlayer level, which become problems in a pattern with processed dimensions not more than several times the wavelength of exposing light.
Further, since correction is carried out after extracting a range requiring correction, correction of a photomask pattern can be carried out efficiently, thereby realizing fast correction of a photomask pattern.
Also, the described arrangement includes an optical proximity effect correcting section which basically carries out correction with respect to the optical proximity effect in a photoresist, thereby realizing accurate photomask pattern correction for the optical proximity effect in a photoresist.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.